The invention pertains generally to hydraulically actuated friction clutches in which pressure fluid is supplied to a hydraulic cylinder to actuate the piston, the fluid being introduced from near the centerline of the clutch and directed radially outwardly where it enters the expansible fluid chamber formed by the cylinder and piston. These clutches thereby have a generally radially extending column of fluid which is subjected to centrifugal force and develops a considerable head acting on the piston, in excess of control pressure applied to the fluid. To balance or compensate for this centrifugal head of the column of fluid, various attempts have been made to solve this problem by the use of centrifugally operated valves such as shown in the U.S. Pats. to C. R. Hilpert Nos. 3,368,656 of Feb. 13, 1968; or 3,358,796 of Dec. 19, 1967. These devices worked very satisfactory for their intended purposes.
In addition, the following U.S. patents are also examples of prior art hydraulically actuated friction clutches having centrifugally operated valves for control thereof and in which the valve mass is affected by centrifugal force.
The Hilpert U.S. Pat. No. 3,578,120, issued May 11, 1971, entitled "Torque Transmission having Acceleration Responsive Fluid Control", utilizes various weights which are designed to be sensitive to angular acceleration and which operate on the centrifugal valves to control acceleration.
The Hilpert U.S. Pat. No. 3,352,395, issued Nov. 14, 1967, entitled "Friction Clutch having Centrifugally Operated Valve Means" utilizes compensating pins to provide stability to the control valve and without those pins the valve would be uncontrollable at certain conditions. These pins however do not counteract the centrifugal forces in the valve system, but do compensate for the change in centrifugal effect on the valve due to radial movement of the valve.
The Groves U.S. Pat. No. 3,913,715, issued Oct. 21, 1975, entitled "Modulatable Friction Clutch Controlled by a Centrifugal Force and Angular Acceleration Sensitive Valve", is somewhat similar to the above Hilpert U.S. Pat. No. 3,578,120, but this Groves patent has weights which are sensitive to both centrifugal force and angular acceleration. The centrifugal force component is used as a speed control and the angular acceleration component has a damping device and torque control.
The U.S. Pat. to Snoy No. 3,534,840 which issued Oct. 20, 1970 and entitled "Hydraulically Actuated Clutch Having A Two Piece Feed Back Dump Valve", by its nature is effected by centrifugal force acting on the mass of the valve parts which causes the clutch to have reduced capacity with increasing speed to a point, where at some speed the clutch has zero capacity. That patent does not have intentional centrifugal force sensitive or angular acceleration sensitive components.
All of the above patents have been assigned to an assignee common with the present invention.
The present invention is also an improvement in certain respects over the subject matter of the U.S. pending application Ser. No. 850,961 (Group 350) filed Nov. 4, 1977, which issued Feb. 5, 1980 as U.S. Pat. No. 4,186,829, of Schneider et al, which has been assigned to an assignee common with the present invention, and in which the trigger pressure falls off with an increase in rotational speed of the clutch.